I too have a surveyor sport with the gas struts on the bed. And the first time I opened my compartment up, I too noticed it was very hard to close. So first thing to check is if the struts are bent. In all likelihood, they are OK and clean. The other issue is they are likely at pristine full factory pressure. Meaning they are at full force so you'll need to strong-arm them. On one side of the bed, place your hand on the plywood under-bed right above the strut and in the direction of the strut, put your weight into it and push hard. You'll find the spring will eventually compress. If you place your hand directly over the strut connection (and directly on the plywood), you should be fine pushing with all your weight. Do this to each side. The second time, you know how much force to use and can press down directly on the mattress to close it - should be easier to close. Do not apply any lubricant or de-greaser to the strut as this might eventually deteriorate the strut seals.
In the end, if something does go wrong, these struts are fairly inexpensive and can be replaced. So give it a go ... and happy camping.